Cellular basis of allograft rejection in vivo. V. Examination of the mechanisms responsible for the differing efficacy of monoclonal antibody to CD4+ T cell subsets in low- and high-responder rat strains

MRC OX35, an anti-CD4 mAb, was used to treat high responder Wistar Furth (W/F) (RT1u) and low responder DA (RT1a) rats which had been grafted with directly vascularized hearts from PVG (RT1c) rats across a full MHC plus non-MHC incompatibility. Four doses of mAb at 7 mg/kg given in the first 2 wk postgrafting induced indefinite graft survival (greater than 150 days) in DA hosts, but only delayed rejection to 18 to 42 days in W/F as compared to rejection times of 6 to 8 days in untreated rats. The extension of MRC OX35 treatment to 6 wk in W/F rats induced indefinite graft survival in three of six rats. During treatment MRC OX35 therapy only partially depleted CD4+ cells, and all circulating CD4+ cells were coated with MRC OX35. The capacity of naive CD4+ and CD8+ cells from W/F and DA to be activated to PVG alloantigen was compared both in vitro in an MLC assay and in vivo by an adoptive transfer assay of their capacity to restore rejection of PVG heart grafts in irradiated syngeneic hosts. CD4+ cells from both W/F and DA proliferated in MLC and restored graft rejection. W/F CD8+ cells both proliferated in MLC and restored rejection, but DA CD8+ cells neither proliferated nor reconstituted rejection. Examination of lymphocytes from MRC OX35 treated hosts with long-surviving grafts showed that they were neither depleted of CD4+ T cells nor did they lack the capacity to proliferate to PVG Ag in MLC, this response being similar to that to third-party Ag or by naive lymphocytes. Compared to first-set rejection, PVG skin graft rejection was delayed 2 to 3 days in W/F and 10 to 12 days in DA rats with long-surviving grafts after MRC OX35 therapy, whereas they rejected third-party skin grafts in first-set tempo. These studies show that differences in graft survival in anti-CD4 treated low and high responder strains may be due to the inherent capacity of CD8+ cells to be activated to effect rejection independent of CD4+ cells in W/F but not in DA. In those hosts that accept grafts, there is no evidence of clonal deletion, but there appears to be a form of unresponsiveness akin to that induced in adult rats by other immunosuppressive therapies that protects the graft from rejection.     

Characterization of the MRC OX40 antigen of activated CD4 positive T lymphocytes--a molecule related to nerve growth factor receptor.

The antigen recognized by the monoclonal antibody (mAb) MRC OX40 is present on activated rat CD4 positive T lymphocytes but not other cells. cDNA clones were isolated from an expression library using the MRC OX40 mAb and the protein sequence for the OX40 antigen deduced. It contains a typical signal sequence and a single putative transmembrane sequence of 25 predominantly hydrophobic amino acids giving an extracellular domain of 191 amino acids and a cytoplasmic domain of 36 amino acids. The sequence of the extracellular domain includes a cysteine-rich region with sequence similarities with the low affinity nerve growth factor receptor (NGFR) of neurons and the CD40 antigen present on human B cells. Within this region three cysteine-rich motifs can be recognized in OX40 compared with four similar motifs in both NGFR and CD40. OX40, CD40 and NGFR constitute a new superfamily of molecules with expression including lymphoid cells (OX40, CD40) and neuronal cells (NGFR). This is reminiscent of the immunoglobulin superfamily whose molecules are variously found at the surface of lymphoid or brain cells or both.     

Expression of the rat CD26 antigen (dipeptidyl peptidase IV) on subpopulations of rat lymphocytes.

The T cell activation antigen CD26 has been recently identified as the cell surface ectopeptidase dipeptidyl peptidase IV (DPP-IV). DPP-IV is found on many cell types, including lymphocytes, epithelial cells, and certain endothelial cells. The MRC OX61 monoclonal antibody (MAb) which specifically recognises rat DPP-IV was used to examine the expression of CD26/DPP-IV on rat lymphocytes. The molecular nature of the antigen was examined by immunoprecipitation from thymocytes, splenocytes, and hepatocytes. Analysis by one- and two-dimensional gel electrophoresis indicated that the native form of CD26 includes a 220-kDa homodimer. On tissue sections MRC OX61 MAb stained nearly all thymocytes and in the spleen and lymph nodes predominantly stained the T cell areas. However, in immunofluorescence experiments OX61 stained 80 to 87% of lymph node cells and 78 to 85% of spleen cells. Furthermore, two-colour immunofluorescence analysis of the CD4+, CD8+, and Ig+ lymphocyte subsets indicated that only 2 to 5% of each of these subsets lacked OX61 staining. Spleen cells and thymocytes of both CD4+ and CD8+ subsets stained much more intensely with OX61 after these cells were stimulated with phytohemagglutinin. These findings indicate that rat CD26 antigen expression is not confined to the T cell population as has been suggested, but also occurs on B cells, and is increased on T cells following their activation.     

Lymphocyte-mediated cytotoxicity: effects of ageing, adult thymectomy and thymic factor.

Adult thymectomy, as well as ageing, depressed splenic lymphocyte-mediated cytotoxicity (LMC) in the mouse. Ageing depressed significantly LMC as early as 19 weeks of age, independently of the number of cells used for immunization. Thymectomy affected LMC only when supoptimal numbers of immunizing allogeneic cells were used. This effect peaked at 6 to 12 weeks after thymectomy. No difference between thymectomized and normal mice was observed when LMC was tested 16 to 20 weeks after thymectomy, at an age when normal control mice themselves already showed a lowered LMC due to ageing. The effect of in vivo treatment with a circulating thymic factor (TF), which was shown to disappear with ageing as well as after adult thymectomy, has been tested in adult thymectomized mice and normal young and ageing mice. TF treatment prevented LMC depression in adult thymectomized mice, whereas it depressed paradoxically splenic LMC in normal young and old mice. The possible mechanisms of the effects of adult thymectomy, ageing, and thymic factor on the different T cell subsets involved in allogeneic killer cell generation are discussed.     

Orexin-A does not stimulate food intake in old rats

Aging is associated with a progressive decrease in appetite and food intake. Both A and B orexins, expressed in specific neurons of the lateral hypothalamic area, have been implicated in the regulation of sleep and feeding. In this study, the stimulatory effect of intracerebroventricular administration of the orexins on food intake was compared between young (4-mo-old) and old (25- to 27-mo-old) male Wistar rats. A stainless steel cannula was implanted stereotactically into the left lateral ventricle. After a 7-day recovery period, different doses (0-30 nmol) of orexins were injected into the left lateral ventricle without anesthesia. Food and water consumptions were measured at 1, 2, and 4 h after injection. The protein levels of orexin receptors, a specific receptor for orexin-A (OX1R) and a receptor for both orexin-A and -B (OX2R), in the hypothalamus were determined by Western blot analysis and compared between young and old rats. Intracerebroventricular administration of orexin-A stimulated food intake in a dose-dependent manner in young rats. However, no effects were observed at any dose in old rats. The protein level of OX1R in the hypothalamus was significantly lower in old rats than in young rats, although the protein level of OX2R was comparable between groups. Results of the present study indicate that the function of the orexin system is diminished in old rats. The decrease in the OX1R protein level in the hypothalamus could be responsible for orexin-A's lack of stimulation of food intake in old rats.     

Class II MHC-expressing cells in the rat adrenal gland defined by monoclonal antibodies

 The detailed distribution and heterogeneity of various immunocompetent cells were characterized in the normal adrenal gland of the rat, with special emphasis on major histocompatibility complex (MHC) class II-expressing cells and macrophages. All adrenals contained at least two different populations of cells reactive with the dendritic cell or the macrophage antibodies. These cells were clearly distinguished from adrenal parenchymal cells by their morphology and location. The majority of dendritic cells were immunoreactive for the MHC class II (Ia) antigen (MRC OX6) and/or the dendritic cell antibodies (MRC OX62), and negative for the macrophage antibodies (ED1, ED2, and/or MRC OX42), whereas the main population of macrophages was immunonegative for the former antibodies and positive for the latter. The OX62-positive cells and the OX42-labeled cells occurred exclusively throughout the medulla. The cellular density of dendritic cells in the adrenal cortex was significantly higher than that of macrophages. Double-immunoperoxidase staining for ED1 and OX6 revealed that positively stained cells could be classified into the following categories: ED1⁺OX6⁺, ED1⁺OX6⁻, and ED1⁻OX6⁺. More then 40% of OX6⁺ cells were immunoreactive for ED1 in the zona glomerulosa, while approximately 15%, 20%, and 30% of OX6⁺ cells were positive for ED1 in the zona fasciculata, zona reticularis and medulla, respectively. ED1⁺ED2⁻ cells were more frequently detected in the zona glomerulosa than in other adrenal zones. Only a few ED1⁻ED2⁺ cells were located in the zona glomerulosa, whereas a large number of them were found in the zona fasciculata. In the zona reticularis and medulla, ED1⁺ED2⁺, ED1⁺ED2⁻, and ED1⁻ED2⁺ cells were detected in the ratio 2:1:3. Our rsults suggest that dendritic cells and macrophages mature during their migration within the adrenal gland. These immunocompetent cells may contribute to a paracrine regulation of adrenal function under physiological conditions. Accepted: 3 November 1997     

Cyclosporine and the thymus: influence of irradiation and age on thymic immunopathology and recovery

With the proper experimental conditions, previous studies have demonstrated that syngeneic and autologous radiation chimeras treated with cyclosporine (CsA) routinely develop a syndrome resembling graft-vs-host disease (GVHD) after CsA is discontinued. The thymus is clearly important in the pathogenesis. Thymectomy prior to CsA prevents the development of syngeneic GVHD and the process can be adoptively transferred via thymocytes. The thymus, however, must be within the field of irradiation and the animal must be young. Here we examine how irradiation and advanced age influence the thymic immunopathologic changes induced by CsA and influence the recovery post-CsA. Young LEW rats, with or without pre-CsA mediastinal irradiation, demonstrate a marked involution of the thymic medulla with associated loss of medullary epithelium, Hassall's corpuscles, class II antigen expression, and maturation of thymocytes. While the control group underwent rapid and complete regeneration of the medulla post-CsA, however, the medullary changes in the irradiated group were prolonged or permanent. Most of these animals had changes of chronic GVHD. Older LEW rats had a more prominent medulla prior to CsA. In contrast to younger rats, the medulla did not show significant involution with CsA. While the Hassall's corpuscles disappeared, the medullae still had fusiform epithelium, dendritic cells, and class II antigen expression. Phenotype stains demonstrated many mature-appearing CD4+/CD8- lymphocytes. In light of evidence indicating the importance of the medullary microenvironment to the maintenance of self tolerance, the medullary effects of CsA are most likely essential to the development of autoimmunity. Young rats rapidly lose the ability to maintain tolerance. While unirradiated rats rapidly reestablish the proper microenvironment following CsA, irradiated rats have a prolonged loss. Older rats may resist the development of autoimmunity by retaining the medullary microenvironment.     

Characterization of rat OX40 ligand by monoclonal antibody

OX40 (CD134) is a member of the tumor necrosis factor (TNF) receptor superfamily first identified as a rat T cell activation marker. We previously identified the rat ligand for OX40 (OX40L) by molecular cloning. In the present study, we newly generated an anti-rat OX40L mAb (ATM-2) that can inhibit the binding of OX40 to rat OX40L and thus efficiently inhibits the T cell costimulatory activity of rat OX40L. Flow cytometric analyses using ATM-2 and an anti-rat OX40 mAb (MRC OX40) indicated that OX40 was inducible on splenic CD4(+) T cells by stimulation with immobilized anti-CD3 mAb, while OX40L was not expressed on resting or activated T cells. OX40L was expressed on splenic B cells after stimulation with lipopolysaccharide (LPS), but not on peritoneal macrophages. Interestingly, splenic dendritic cells (DC) expressed OX40L constitutively, which was further upregulated by LPS stimulation. The potent costimulatory activities of splenic DC for anti-CD3-stimulated rat CD4(+) T cell proliferation and cytokine (IL-2, IFN-gamma, IL-10, and IL-13) production were substantially inhibited by ATM-2. These results indicated that OX40L is expressed on professional antigen-presenting cells (APC), and may be involved in humoral immune responses via T-B interaction and in cellular immune responses via T-DC interaction in the rat system.     

Involution of the rat thymus in experimentally induced hypothyroidism

The thymus, as part of the immune-neuroendocrine axis, is greatly influenced by factors from most endocrine glands, especially the thyroid. Antithyroid drugs (carbimazole and methimazole) were used to induce hypothyroidism in rats. Histological and ultrastructural examination of the thymus showed progressive thymic involution after 4 weeks of drug treatment to the end of observations (7 weeks). The involution was characterised by increased thymocyte apoptosis and thymocyte phagocytosis by macrophages. This resulted in thymocyte depopulation, increases in numbers of interdigitating cells, alterations to mainly subcapsular and medullary epithelial cells, an apparent increase of mast cells and collagen in the capsule and septa, and increased numbers of B cells and plasma cells. Lymphoid cells immuno-reactive with MRC OX12 (which detects B cells) were observed within blood vessel walls, suggesting that they may have been moving in and out of the thymus. The administration of drugs causing hypothyroidism, therefore, also caused marked involution of the thymus.     

Age-associated thymic atrophy is not associated with a deficiency in the CD44(+)CD25(-)CD3(-)CD4(-)CD8(-) thymocyte population.

Age-associated thymic atrophy has been proposed to be due to changes in both the thymic microenvironment and in the intrinsic properties of the early T cell progenitors, the CD44(+)CD25(-)CD3(-)CD4(-)CD8(-) cells. We have purified these cells from the thymus of both old and young mice and demonstrate no age-associated defect in their ability to differentiate into their progeny in vitro when used to reconstitute fetal thymic organ cultures. We also demonstrate that in the presence of anti-IL-7, CD44(+)CD25(-)CD3(-)CD4(-)CD8(-) cells from young mice show reduced thymocyte development in fetal thymic organ cultures compared with controls. Finally we have shown that old mice treated with IL-7 show improved thymopoiesis compared with control groups. The increased thymopoiesis seen in the old animals occurs in the sequential manner which would be anticipated for an agent working directly on the early stages, including the CD44(+)CD25(-)CD3(-)CD4(-)CD8(-) cells.     

Interleukin 1beta as stimulator of the rat thymus

The effects of interleukin 1beta administration on the thymus of adult and old rats were studied in order to study the interactions between the nervous and immune systems and to confirm the important role played by catecholaminergic nerve fibres (CNF) in the regulation of thymic functions. Moreover, chemical sympathectomy was performed in a group of rats to study the effects on thymus of the destruction of the majority of CNF. Our results indicate that thymic stimulation (performed by means of interleukin 1beta) induces substantial changes in the fresh weight of the whole thymus, as well as in the thymic microenvironment, thymic nerve fibres, CNF, neuropeptide Y (NPY)-like positive nerve fibres and total amount of both proteins and norepinephrine in rat thymic tissue homogenates. The majority of CNF are destroyed after chemical sympathectomy with 6-OH-Dopamine (DA) and remain unchanged after treatment with interleukin 1beta.     

猫小脑髓质胶质反应的年龄相关性变化

探讨青年猫和老年猫小脑髓质中胶质反应的年龄相关性变化及其意义。用改良的Holzer结晶紫染色显示所有胶质细胞,GFAP(胶质纤维酸性蛋白)免疫染色显示星形胶质细胞。光镜下对青年猫与老年猫小脑髓质中胶质细胞和GFAP免疫阳性(GFAP-IR)星形胶质细胞进行形态学观察和定量研究。与青年猫比较,老年猫小脑髓质中胶质细胞和GFAP-IR细胞密度均显著增加(P<0.01),胞体较大;GFAP阳性细胞阳性反应较强,突起稠密;星形胶质细胞占胶质细胞总数比例增加。这表明小脑髓质中胶质细胞随年龄增长明显增生,尤其星形胶质细胞具有明显的年龄相关性活动增强。提示胶质细胞及星形胶质细胞的增生可能对衰老的神经纤维起保护作用;星形胶质细胞对衰老较敏感。     

Caloric restriction maintains OX40 agonist-mediated tumor immunity and CD4 T cell priming during aging

Immune responses wane during aging, posing challenges to the potential effectiveness of cancer immunotherapies. We previously demonstrated that in the context of a promising immunotherapeutic, OX40 agonist (αOX40), older animals exhibited impaired anti-tumor immune responses and diminished CD4 T cell effector differentiation. In this study, we hypothesized that tumor immune responses could be maintained during aging through caloric restriction (CR) or dietary supplementation with resveratrol (RES), a CR mimetic. Mice were placed on either a calorically restricted diet or a RES-formulated diet starting between 4 and 6 months of age and continued until mice reached 12 months of age. Tumor immune responses were assessed after challenging with either sarcoma or breast tumor cells followed by αOX40 treatment. Our results show that CR, but not RES, maintained OX40-mediated anti-tumor immunity. In addition, CR fully sustained antigen-specific CD4 T cell priming in aged hosts (12 months old), whereas tumor-specific CD8 T cell priming was not fully maintained compared to young reference animals (2 months old). Thus, CR appears to maintain immunological fitness of the CD4 T cell priming environment during aging, which is critical for optimal OX40-mediated responses.     

Expression of PAC1 receptor in rat thymus after irradiation

In the present work, PAC1-R (G-protein-coupled receptor specific for PACAP) was detected on cells in the normal thymus. Immunohistochemically PAC1-R was expressed strongly in stromal cells of the thymic medulla. Positive cells were also observed in the thymus of fetal and old adult rats. After 8 Gy irradiation to 9-week-old rats, PAC1-R expressions in the thymus decreased and almost recovered by day 21. The expression of PAC1-R mRNA was weak in the thymus and decreased further after irradiation. The expression almost recovered by day 28. Hip and hip/hop variants, which were not expressed in the normal thymus, were expressed in the thymus on days 3, 5 and 21 after irradiation. The expressions of IL-6 and IL-10 tended to increase initially after irradiation then decreased. Histologically, the thymic structures were destroyed on day 3 after irradiation and the thymus almost recovered by day 21. Thus PACAP is thought to be one of the important factors for cross-talk between cells involved in thymic regeneration.     

Lymphohematopoietic progenitors do not have a synchronized defect with age-related thymic involution

It has been speculated that aging lymphohematopoietic progenitor cells (LPC) including hematopoietic stem cells (HSC) and early T-cell progenitors (ETP) have intrinsic defects that trigger age-related thymic involution. However, using a different approach, we suggest that that is not the case. We provided a young thymic microenvironment to aged mice by transplanting a fetal thymus into the kidney capsule of aged animals, and demonstrated that old mouse-derived LPCs could re-establish normal thymic lymphopoiesis and all thymocyte subpopulations, including ETPs, double negative subsets, double positive, and CD4(+) and CD8(+) single positive T cells. LPCs derived from aged mice could turn over young RAG(-/-) thymic architecture by interactions, as well as elevate percentage of peripheral CD4(+)IL-2(+) T cells in response to costimulator in aged mice. Conversely, intrathymic injection of ETPs sorted from young animals into old mice did not restore normal thymic lymphopoiesis, implying that a shortage and/or defect of ETPs in aged thymus do not account for age-related thymic involution. Together, our findings suggest that the underlying cause of age-related thymic involution results primarily from changes in the thymic microenvironment, causing extrinsic, rather than intrinsic, defects in T-lymphocyte progenitors.     

斜带石斑鱼胸腺的显微和超微结构

本文通过解剖及组织切片技术、光学显微镜、透射和扫描电子显微镜技术,对斜带石斑鱼(Epinephelus coioides)胸腺器官组织进行了观察研究。结果表明:斜带石斑鱼胸腺实质主要由胸腺细胞(淋巴细胞)和网状上皮细胞构成。鱼体从Ⅰ龄之后,其胸腺发生明显的变化,与幼鱼有所不同,主要是胸腺可明显区分为三个区域:胸腺外皮质区、内皮质区和髓质区。外皮质区主要由网状上皮细胞、黏液细胞、成纤维细胞和少量淋巴细胞构成,细胞排列疏松;内皮质区主要由密集的淋巴细胞和网状上皮细胞组成,以含有大量的淋巴细胞为特征;髓质区主要由淋巴细胞和较多的网状上皮细胞构成,总体特征是淋巴细胞数量比内皮质区的少,且细胞排列较疏松。外皮质区、内皮质区相当于高等脊椎动物的皮质;髓质区相当于高等脊椎动物的髓质。髓质区之下有结缔组织,在Ⅱ龄以上的成体出现胸腺小体(Hassall's corpuscles)或类似胸腺小体的结构,而且随着年龄的增加,胸腺外皮质区增厚,结缔组织增加,还表现在内皮质区和髓质区组织逐渐萎缩变薄,胸腺的细胞组成类型和淋巴细胞数量上有所变化等等。这些现象在Ⅱ龄鱼开始出现,即胸腺呈现退化迹象,在Ⅲ龄以上鱼体呈现明显的退化和萎缩。胸腺表面扫描电镜结果表明:其上皮细胞表面具有微嵴以及由微嵴组成的指纹状结构,有一些微孔分布。透射和断面扫描电镜的结果进一步表明:胸腺组织内的细胞成分复杂,除了淋巴细胞和网状上皮细胞外,还具有巨噬细胞、肥大细胞、肌样细胞、浆细胞、指状镶嵌细胞和纤维细胞等。     

In vivo treatment with anti-CD8 and anti-CD5 monoclonal antibodies alters induced tolerance to adjuvant arthritis

Resistance (low dose tolerance) to adjuvant arthritis was induced by intradermal immunization with 10 micrograms Mycobacterium tuberculosis administered 5 and 3 weeks before induction of arthritis. With the purpose of determining phenotypes of cells which participate in the maintenance of the induced resistance to adjuvant arthritis, tolerized rats were treated with two different anti-T-cell monoclonal antibodies. In tolerized rats, it was shown that anti-CD8 (OX8) antibodies, which caused an elimination of CD8+ lymphoid cells as determined by immunofluorescence analysis, made the rats responsive to an arthritogenic challenge with mycobacteria. Nine of 19 (47.4%) rats developed the disease as compared with 2 of 18 (11.1%) (P less than 0.05) in the control antibody-treated group. Also, in vivo treatment with anti-CD5 (OX19) monoclonal antibodies made the rats responsive to an arthritogenic challenge with mycobacteria. Nine of 15 (60%) anti-CD5-treated rats developed the disease as compared with 2 of 18 (11.1%) (P less than 0.01) rats in the control group. Immunofluorescence analysis performed after anti-CD5 treatment showed a reduction of staining of CD5+ cells as well as a down-regulation of the staining intensity of CD5 cell surface receptors on the remaining CD5+ cells. These data indicate that CD8+- as well as CD5+ cells participate in the maintenance of low dose tolerance to adjuvant arthritis.     

Selective induction of OX19+ (CD5+) or OX19- (CD5-) alloreactive cytolytic lymphocytes in the rat

The phenotypes of alloselective cytolytic lymphocytes of the rat are defined by staining of peritoneal cells of alloimmunized donors with monoclonal antibodies, sorting in a cytofluorometer and evaluating cytolytic capacity in a 51Cr-release assay. We demonstrate that alloimmunization of BN rats can result in either OX19+ (CD5+) or OX19- (CD5-) cytolytic alloselective lymphocytes and show that the OX19- (CD5-) cytolytic cells are OX34+ W3/25- (CD4-) OX8+ (CD8+) lymphocytes not exposing surface Ig. It is further demonstrated that the appearance of CD5+ and CD5- cytolytic alloselective lymphocytes are mutually exclusive; immunization with (WF X BN) F1 cells leading exclusively to appearance of OX19+ effector cells while immunization with WF cells leads to OX19- effector cells. Alloimmunization of WF rats only results in appearance of OX19+ cytolytic lymphocytes.     

Uremia causes premature ageing of the T cell compartment in end-stage renal disease patients

ABSTRACT: BACKGROUND: End-stage renal disease (ESRD) patients treated with renal replacement therapy (RRT) have premature immunologically aged T cells which may underlie uremia-associated immune dysfunction. The aim of this study was to investigate whether uremia was able to induce premature ageing of the T cell compartment. For this purpose, we examined the degree of premature immunological T cell ageing by examining the T cell differentiation status, thymic output via T cell receptor excision circle (TREC) content and proliferative history via relative telomere length in ESRD patients not on RRT. RESULTS: Compared to healthy controls, these patients already had a lower TREC content and an increased T cell differentiation accompanied by shorter telomeres. RRT was able to enhance CD8+ T cell differentiation and to reduce CD8+ T cell telomere length in young dialysis patients. An increased differentiation status of memory CD4+ T cells was also noted in young dialysis patients. CONCLUSION: Based on these results we can conclude that uremia already causes premature immunological ageing of the T cell system and RRT further increases immunological ageing of the CD8+ T cell compartment in particular in young ESRD patients.     

Thyroid C cell function during fasting and refeeding of young and old rats

Age-related alterations in the structure and function of many organs often become apparent under stimulation of their function. Although the ageing process affects the regulation of mineral homeostasis, the function of thyroid C-cells that secrete calcitonin (CT) under the conditions of fasting and refeeding, a way of dietary manipulation that reveal the existence of age-related changes of follicular thyroid cells, has not been characterized. Therefore, we investigated the number of C-cells and serum CT concentration in young (4 mo) and old (26 mo) male rats fasted for 48 hours, and then refed for 4 or 24 hours. We found significantly higher number of C-cells in thyroids of old vs young rats both under basal conditions, and after fasting/refeeding. Correspondingly, serum calcitonin level was higher in fed or fasted old rats vs young ones. However, in young rats refeeding decreased, whereas in old animals increased serum concentrations of calcitonin. Thus, the control of serum calcium concentration, that was well preserved in old rats, occurs at the expense of increased serum CT level both under basal conditions, and after refeeding. These observations suggest that C-cell function is altered in ageing.